1. Field of the Invention
The present invention relates to electromagnetic sensing of damage and/or deterioration of objects made of, or incorporating, a magnetically permeable material, such as an elongate conveyor belt where reinforcing cables made of the magnetically permeable material are imbedded in (and thus largely concealed in) a relatively nonpermeable material such as a rubber-like structure of the belt.
2. Background Art
Large conveyor belts are used in a variety of applications, one of the major applications being in the mining industry where metal ore or other material is carried from the mine to a collecting location. For example, in an open pit mine, it is not uncommon to have a conveyor belt extending from a lower location upwardly for a distance as long as several thousand feet or even several miles. Such belts can possibly be as large as eight feet wide, and possibly as thick as four inches. The main belt material generally is a moderately flexible rubber-like material, and the belt is reinforced by a plurality of longitudinally extending metal cables which are positioned within the belt and extend along the length thereof.
One of the problems is that after continued use the metal reinforcing cables will deteriorate. For example, there may be a break in the conveyor belt material that would permit water or possibly even an acid (e.g. resulting from water reacting with the conveyed material) to come in contact with one or more of the cables to corrode the cables. The damage to the cables could come from an impact of some sort, or the deterioration could occur from natural wear or possibly fatigue of the metal because of long continued use. Sometimes the damage to the cable is a total break, and in some instances a partial deterioration that simply weakens the belt.
Since the metal cables in the belt are not visible, it is difficult to detect much of the damage to the cables. Unfortunately, when the damage is sufficiently severe so that it becomes outwardly visible, there may already have been a condition which would make further use of the belt dangerous. For this reason, it has usually been a practice in the industry to in a sense "overdesign" the belts so that there would be an adequately large margin of error to enable the belt to still function reasonably safely, even though there had been substantial degradation of the reinforcing cables.
Accordingly, an improved means of sensing deterioration (even a relatively small amount of deterioration) at an earlier time when it would not be visible by inspecting the outside of the belt would be advantageous.